Method of improvement of heat transfer coefficient in heat exchangers



United States Patent 3,006,858 METHOD 9F H/IPRQVEMENT OF HEAT TRANS- FEB; CQEFFECIENT IN HEAT EXCHANGERS David B. Boies, Chicago, 111., assignor to Nalco Chemical Company, a corporation of Delaware No Drawing. Filed Jan. 2, 1958, Ser. No. 706,553 7 Claims. (Cl. 252-73) This invention relates to a method of increasing the heat transfer coefiicient in heat exchangers wherein petroleum hydrocarbons are in contact with metal surfaces of heat exchangers under relatively high temperature conditions. Normally, the metal surfaces of heat exchanger Walls become contaminated during the manufacture of petroleum products. The contamination causes the heat transfer coefiicient to fall off rapidly thereby reducing the efiiciency of the unit.

More particularly, this invention relates to a method of increasing the heat transfer rate between heated metal surfaces of conduits and petroleum hydrocarbons flowing therethrough by the inclusion in the hydrocarbon liquid of minor amounts of an additive which initially increases the heat transfer coefiicient. Additionally, the invention is directed to a combination of additives which, when included in the hydrocarbon liquid being heated, not only contribute to an increase in the heat transfer coefficient of the heat exchanger, but act as well to prevent subsequent decline in value of the heat transfer coefficient.

It is, therefore, the primary object of this invention to provide a means for increasing the heat transfer coefiicient in heat exchangers used in treating petroleum hydrocarbons by inclusion in the oil being heated of a relatively minor quantity of readily available inexpensive additive.

It is a further object of this invention to include with the primary additive a second or synergistic additive which additives, acting in combination, both initially increase the heat transfer coefficent and tend to maintain the heat transfer coeflicient over long periods of time during continuous operation of the unit.

Another object of the invention is to provide a practical and economic means of treating petroleum hydrocarbons prior to entry into heat exchange equipment to prevent the insulative deposits on the metal surfaces of heat exchangers and to provide a greater eificiency of heat transfer from the walls of the exchanger to the petroleum hydrocarbon flowing in contact with said walls without interfering with continuous processes by shutdown of the heat exchange equipment.

Other objects and advantages of the method herein described will appear as the details of the invention are set forward.

The principal object of this invention is accomplished, namely that of increasing the efiiciency of heat transfer in an oil heating heat exchanger, by inclusion in the flowing hydrocarbon oil stream from about .25 to 1% of water, based upon the weight of the hydrocarbon oil being processed. The addition of effective amounts of water to the liquid hydrocarbon can be accomplished by a number of methods well established in the art.

In the preferred practice of the invention, a combination of additives has been found to be synergistically useful to accomplish the objective of both increasing the heat transfer coefiicient and to maintain the increased heat transfer coeficient at a level above that heretofore possible to maintain during continuous heating operations wherein a hydrocarbon oil is heated by contact with the metal walls of heat exchangers.

The second additive, which is used in extremely minute quantity, is an organic compound from the class generally described as detergents and which are used in conjunction with the water treatment in an amount from about 0.1% to about 20% by weight of the added water. More or less may be used, but as cost is a factor little advantage is deemed to be obtained by inclusion of amounts greater than about 20% of detergent based on the water added.

Strangely, not .all surface active agents are useful for the purpose and the theory behind their effectiveness is, therefore, not apparent. It has been found by testing species of a wide variety of classes of surface active agents that only those that are generally classed as detergents are useful for the purposes of this invention. The particular agents within the detergent class have been identified by some workers concerned with the problem of classification of surface active agents as those having a particular balance between the hydrophilic portion of the molecule and the lipophilic portion of the molecule. The subject of hydrophilic-lipophilic balance has been discussed in several papers published by Griffin, namely, Calculation of HLB Values of Non-Ionic Surfactants, December 1954, Journal of Society of Cosmetic Chemists, volume 5, Number 4, and in the same Journal but volume 1, Number 5, of December 1949, Classification of Surface Active Agents. The hydrophilic-lipophilic balance is referred to as HLB and certain numbers of HLB have been selected to define the nature of those agents which act as detergents. But even among this group only certain particular materials have been so far found useful at practical concentrations.

When one considers the tremendous volume of hydrocarbon oil processed through heat exchangers, the amount of additives essential to accomplish the ends of this invention must of necessity be economically practicable.

Detergents useful for the purposes of this invention. have been found to contain from 8 to 36 or more carbon atoms in a hydrocarbon structure and a water-soluble group comprising at least two oxyalkylene groups wherein said alkylene groups contain not more than 3 carbon atoms per oxyalkylene group. This hydrocarbon group is preferably attached to a nucleus which, in the parent form of the developed compound, is characterized by the presence of one or more active or labile hydrogen atoms in said nucleus. The most useful class of detergent compositions are derived from the parent compounds by further condensation with one or more active hydrogen atoms of the nucleus thereof with from one to about 15 mols of an alkylene oxide wherein the alkyl group contains not more than 3 carbon atoms and preferably only 2, namely, ethylene oxide. Data presently available indicates that the number of mols of ethylene oxide or 1,2-propylene oxide condensed with the parent long chain alkyl hydrocarbon structure is from one to about 10 mols of the alkylene oxide.

For purposes of visual illustration of the particular class of detergent compositions useful for the purposes of this invention, the following general structure may be helpful:

where R is a hydrocarbon structure containing from 8 to about 36 carbon atoms, M in the parent compound is a nucleus containing from 1 to 3 reactive hydrogen atoms, z is a whole number from 2 to 3, y is a whole number from 2 to 15 and x is a whole number from 1 .to 3 depending upon the number of reactive hydrogen structure. At least one of the reactive hydrogens as sociated with the nitrogen nucleus of the fatty amine is condensed with from 2 to 15 mols of ethylene oxide and preferably about 2 to mols.

A second sub-group of useful detergents includes long chain fatty acid condensation products of alkyl monocarboxylic acids containing from 8 to about 36 carbon atoms in a hydrocarbon structure condensed with 2 to mols of ethylene oxide and preferably from 2 to about 10 mols.

The third sub-class is somewhat anomalous and needs a word of explanation as to the probable theory behind its efiectiveness for the ends of the invention. This agent as added to the hydrocarbon oil is not of itself a detergent. It is well established, however, in the art relating to surface activity that the useful agent is a precursor of a well established class of surface active agents. This class of compounds is referred to generally as polyalkanolamines, all of which are water-soluble. The representative species, namely, triethanolamine, is well known for its reaction products with free fatty acids, in situ, to form detergents. The extreme usefulness of triethanolamine in the present invention suggests that the petroleum hydrocarbons as herein treated contain traces of relatively high molecular weight organic acids. These traces of organic acids are believed to react with the polyalkanolamines, in situ, to form detergent compounds equivalent to or falling within the generic class as identified above.

Another useful'class of surface active agents for the purposes of this invention, which appear to act synergistically with small amounts of water added tohydrocarbon oils, are the condensation products of rosinamines with from 2 to 15 mols of ethylene oxide. One may readily observe the close similarity of the members of this class with those described in the first subgroup. Again, the amount of ethylene oxide is preferably limited to from 2 to about 10 mols.

Familiarity with the above sub-classes led to the trial of a condensation product of aminoethanol amine and a fatty acid containing from 8 to 36 carbon atoms in a hydrocarbon structure, which condensation product may be identified as a l-hydroxyethyl 2-alkyl imidazoline, wherein the alkyl group contains from 8 to 36 carbon atoms.

' Imidazolines of this class are further condensed with from 2 to 15 mols and preferably 2 to 10 mols of ethylene oxide.

These surface active agents were found extremely useful when included with from .25% to 1% of water in an amount from about 0.1 to not more than about by weight of the water treatment as additives in petroleum hydrocarbons to increase and maintain at increased levels the heat transfer coeflicient of hydrocarbons as they are pumped through heat exchangers in petroleum processing.

Having described the general and the sub-generic classes of detergents useful for the purpose of this invention, the following species of each of the classes has been selected as exemplary of the sub-classes and their use demonstrated in trial runs which are hereinafter set forth to illustrate preferred procedures for the practice of the method.

7 An illustrative species of the first class identified as species I-A is the condensation product of a tallow oil fatty amine condensed with '5 mols of ethylene oxide.

Under the second sub-class a species identified as I1-D is a coconut oil fatty acid condensed with 10 mols of ethylene oxide.

Under the third class identified as species III-G is triethanolamine which, as indicated above, is believed to form a triethanolamine salt, in situ, with traces of hydrocarbon acids of unknown but high molecular weight which" are inherently present in the petroleum oils subject to test.

Species IV-A is a condensation product of a mixture of rosin amines (Rosin Amine D) with about 3 mols of ethylene oxide.

Representative of the last sub-class (sub-class V) is the imidazoline formed by condensing oleic acid and aminoethanolamine, further identified as l-hydroxyethyl 2-heptadecenyl imidazoline further condensed with 5 mols of ethylene oxide.

The examples of this invention have been illustrated by a means of actual trial runs set up on a laboratory scale. The equipment, the method of test, and the test results are set forward in the following expository matter:

A laboratory heat exchanger system was set up providing a first circuit consisting of a black iron tube of inch external diameter and /2" internal diameter defining a circuit of about 20 per side of four sides arranged as a square. One side of said circuit is equipped with a circulating pump which recycles the feed stock at a rate of 2 gallons per minute. The feed oil stock is injected by an injection pump into the circuit at a rate of 2 gallons per hour from a feed stock reservoir equipped with a Lightning mixer for treatment purposes. The heat exchanger portion is in the side of the circuit opposite the circulating pump and is constructed as follows:

Wrapped around the middle portion of the external diameter of the black iron tube along 15 inches of the length of one side are three layers of heavy mica over which is wound 36.3 feet of No. 14 Nichrome wire. Means are provided for measuring the heat input. The heater element is covered with a A inch layer of refractory cement and about the outside periphery of the cement is wrapped about 1 inch of insulating composition. The temperature of the heat exchanger tube wall is determined by a thermocouple set down in a hole through the insulation and refractory cement into a /3 inch well drilled into the tube wall wherein the couple is held by brazing. A

' shunt is provided in the main circuit of the same diameter tubing. The shunt circuit is equipped with a pressure gauge, a cooling coil and a pressure relief valve before emptying into a waste collection vessel open to the atmosphere.

Pressure in the unit is maintained at pounds (p.s.i.g.). The temperature of the oil is measured at the outlet end of the heat exchanger. portion of the circuit, also by means of a thermocouple, but extending through the tube wall into the oil stream.

In evaluating the test runs, the heat transfer co-efiicient, U, was determined from the following equation:

Q=UAAT where Q heat input to oil in B.t.u./hr.

U=heat transfer coeflicient in B.t.u./hr./sq. ft./ F.

A=area of heat transfer surface in square feet AT=Temperature differential between the oil circulating temperature T and the wall temperature T in degrees F.

Laboratory Field Unit Test U, B.t.u./hr./sq. ft./ F 56. 7-70. 7 51-83 Velocity of fluids, ft./sec a 0. 5-0. 6 Residence Time in Heat Exchanger, sec 58 30-60 Heat Load, Btu/sq. ft./hr .L 22,180 5-20, 000

In making test runs, a period was allowed in each case for the system to come to equilibrium which was deemed to occur in less than two hours. Drops in the value of U at the end of two hours were calcu-lated from data obtained after that time of run.

In all runs, the water used as additive was Chicago tap water, a typical analysis of which can be found in Langs Handbook of Chemistry, 7th edition, page 784.

Three samples of petroleum hydrocarbons were selected for test purposes: Sample A was a gas oil from an Ohio refinery; sample B was a gas oil from an Indiana refinery of Mid Continent origin; sample C was a gas oil originating from a refinery in Louisiana.

A wide variety of detergent compositions (by this term detergent is meant those surfactants producing the lowest interfacial tension between oil and water as determined by the du Nuoy ring method at a standard 0.5% of the surfactant concentration in the aqueous phase, also identifiable by the hydrophile-lipophile balance by characteristic numbers identified as HLB numbers or HN numbers) were selected for exploratory testing as to their effect upon the heat transfer coefiicient when used in trial runs in a laboratory test unit.

On the basis of this selection of detergents, surprising difierences in test results were observed. There seemed to be little correlation, for many of the materials selected on this basis were ineffective for the purpose of preventing decreases in the value of U with increased length of time of test runs. Thus, not all surfactants having the quality of detergency were useful. Increased heat trans- 5 fer coeflicients, originally obtained by water addition and improve the heat transfer rate even after the flow of additives into the oil has been stopped. Where continued treatment is not economical or practical, for one reason or another, a schedule of intermittent treatment to meet specific conditions in the unit involved is useful. Less effective, but also productive of beneficial efiect upon heat transfer, is the intermittent use of water alone in a 0.25% to about 1% level based on the weight of the oil to be subject to heat treatment. 4

TABLE I Oil sample A Test Concen- Water Oil Run No. Run, Detergent Additration, Added, Ten1p., AT, F. U

Hours tive ppm. Percent F.

of oil 2 None 403 297 73. 7 Run 1 i 3 None 410 337 G5. 3

2 1. 0 445 32 3 1. 0 432 98 227 4 1.0 433 127 176 5 1. 0 438 146 152 6 1. 0 452 163 136 Run N0. 2 7 1. 0 465 133 122 8 1. 0 468 204 109 9 1. 0 472 230 97 10 1. 0 475 253 38 11 1. 0 468 280 12 do 1.0 465 300 74 3 Detelrgent I-A 158 1.8 :70 5 4, 400 4 5 75 10 2, 200 Run 3 5 150 1. 0 477 21 1, 050 150 1. 0 540 10 2, 200

TABLE II Ozl sample B Test Concen- Water Oil Run No. Run, Detergent Additration, Added, Temp., AT, F. U

Hours tive p.p.m. Percent F.

of oil 1 3 32 it? 2 one 36 3 Run 4 3 None 358 334 66. 5 4 None 355 360 62. 0 1 1. 0 415 33 681 2 1. 0 450 2% 1, 835 4 1.0 4 2 2 0 Run 5 6 1. 0 455 23 980 7 0. 5 460 23 776 8 0.5 462 43 523 1 0. 33 435 262 2 8. 33 425 2 1, 430 4 3 4 55 Run 6 5 0. 25 453 167 13s 6 0. 25 460 195 116 6. 5 0. 25 :56 222 11% 6 0. 25 42 5 27 Rm 7 i s 0. 25 46s 70 322 2 0. 25 393 247 91 Run No. 3 3 0. 25 398 214 4 0. 25 408 167 134 2 0. 25 400 200 112. 5 Run N0. 9 3 0. 25 405 177 127 4 0. 25 405 177 127 2 0. 25 412 174 129 Run No. 10 3 0. 25 414 149 151 4 0. 25 422 126 179 TABLE III Oil sample C Test Concen- Water Oil Run No. Run, Detergent Additratiou, Added, Temp., A'I, F. U

Hours tivc ppm. Percent F.

of oil 1 None 443 244 2 None 452 242 91. 5 3 None 442 276 79. 9 4 None 434 324 68.

Run N0. 11 5 0. 400 207 106.2 6 0. 50 410 78 282 7 1.0 413 67 328 8 1.0 409 60 367 9 1. 0 410 61 361 1 O. 5 347 103 2 0.5 380 8 Run 12 3 0. 5 373 so 252 4 0.5 377 95 236 The above tabulated data is not an exhaustive report a of results obtained by practice of the invention herein described. It is, however, generally illustrative of the quality of the result obtained by practice of the invention and briefly illustrative of changes observed by variation in the variables of the process. Obviously, the many permutations and combinations afforded in the conduct of the work summarized above lead to specific combinations of greater or lesser value depending upon the conditions met, the nature of the hydrocarbon oil being processed, rates of flow, AT, etc., as are well understood by those engaged in the art of petroleum processing.

In treatment of. heat exchanger surfaces the problem met is concerned with fouling of the surface by accretion upon the heat transfer surface adjacent the material Whose temperature is.being altered. The problem of prevention of deposition of foreign matter on the walls of the tubes of the heat exchangers during heating and cooling bears little or no relation to the problem of corrosion of heat exchanger tubes wherein an aqueous liquid tends to attack the walls of heat exchangers. The problem of prevention of fouling in non-aqueous systems is not to be confused with prevention of corrosive action in aqueous systems.

Having thus described my invention, what I claim is:

1. A method of increasing the heat transfer coefiicient between a petroleum hydrocarbon oil and the wall of a heat exchanger through which said oil is passed which comprises: feeding into said oil stream a detergent and from 0.25% to about 1% by weight of water, based on the weight of said oil, said detergent being selected from the group consisting of triethanolamine and the condensation product of ethylene oxide and a fatty compound selected from the group consisting of an alkyl amine having from 8 to 36 carbon atoms in its alkyl group, an allcyl monocarboxylic fatty acid having from 8 to 36 carbon atoms in its alkyl group, a rosin amine, and the condensation product of monoethanol amine and an alkyl fatty acid containing from 8 to 36 carbon atoms in its alkyl group; each mol of said fatty compound being condensed with from 2 to 15 mols of ethylene oxide; the quantity of said detergent added to said stream being from about 0.1% to about 20% by weight based on the weight of the added water.

2. A method as in claim 1 wherein from 2 to 10 mols of ethylene oxide are condensed with said fatty compound.

3. A method of increasing the heat transfer coefficient being from about 0.1% to about 20% by weight of said added water.

4. A method of increasing the heat transfer coefficient between a petroleum hydrocarbon oil and the wall of a heat exchanger through which said oil is passed which comprises: feeding into said oil stream a detergent and from 0.25 to about 1% by weight of water, based on the weight of said oil, said detergent consisting of the condensation product of an alkyl monocanboxylic fatty acid containing from 8 to 36 carbon atoms in its alkyl group and from 2 to 15 mols of ethylene oxide; the quantity of said detergent being from about 0.1% to about 20% by weight of said added water.

5. A method of increasing the heat transfer coeflicient between a petroleum hydrocarbon oil and the wall of a heat exchanger through which said oil is passed which comprises: feeding into said oil stream a detergent and from 0.25% to about 1% by weight of water, based on the weight of said oil, said detergent consisting of the condensation product of a rosin amine and from 2 to 15 mols of ethylene oxide; the quantity of said detergent being from about 0.1% to about 20% by weight of said added water.

6. A method of increasing the heat trans-fer coeflicient between a petroleum hydrocarbon oil and the wall of a heat exchanger through which said oil is passed which comprises: feeding into said oil stream a detergent and from 0.25% toabout 1% by weight of water, based on the weight of said oil, said detergent consisting of the condensation product of monoethanolamine and an alkyl fatty acid containing from 8 to 36 carbon atoms in its alkyl group which condensation product is then condensed with from 2 to 15 mols of ethylene oxide; the quantity of said detergent being from about 0.1% to about 20% by weight of said added water.

7. A method of increasing the heat transfer coefficient between a petroleum hydrocarbon oil and the wall of a heat exchanger through which said oil is passed which comprises: feeding into said oil stream uiethanol amine and from 0.25 to about 1% by weight of water, the quantity of said triethanolarnine added to said stream being from about 0.1% to about 20% by weight based on the weight of the added water.

References Cited in the file of this patent UNITED STATES PATENTS 2,150,936 Morgan Mar. 21, 1939 2,328,727 Langer Sept. 7, 1943 9, 84 Barker July 10,1951 2,617,769 7 Nichols NOV. 11, 1952 OTHER REFERENCES Proceedings: Symposium onSaline Water Conversion, 1957, publication 568, National Academy of Sciences, National Research Council; Washington, DC. (1958), Pag s 4 74, 75, 423 and 424. 

1. A METHOD OF INCREASING THE HEAT TRANSFER COEFFICIENT BETWEEN A PETROLEUM HYDROCARBON OIL AND THE WALL OF A HEAT EXCHANGER THROUGH WHICH SAID OIL IS PASSED WHICH COMPRISES: FEEDING INTO SAID OIL STREAM A DETERGENT AND FROM 0.25% TO ABOUT 1% BY WEIGHT OF WATER, BASED ON THE WEIGHT OF SAID OIL, SAID DETERGENT BEING SELECTED FROM THE GROUP CONSISTING OF TRIETHANOLAMINE AND THE CONDENSATION PRODUCT OF ETHYLENE OXIDE AND A FATTY COMPOUND SELECTED FROM THE GROUP CONSISTING OF AN ALKYL AMINE HAVING FROM 8 TO 36 CARBON ATOMS IN ITS ALKYL GROUP, AN ALKYL MONOCARBOXYLIC FATTY ACID HAVING FROM 8 TO 36 CARBON ATOMS IN ITS ALKYL GROUP, A ROSIN AMINE, AND THE CONDENSATION PRODUCT OF MONOETHANOL AMINE AND AN ALKYL FATTY ACID CONTAINING FROM 8 TO 36 CARBON ATOMS IN ITS ALKYL GROUP, EACH MOL OF SAID FATTY COMPOUND BEING CONDENSED WITH FROM 2 TO 15 MOLS OF ETHYLENE OXIDE, THE QUANTITY OF SAID DETERGENT ADDED TO SAID STREAM BEING FROM ABOUT 0.1% TO ABOUT 20% BY WEIGHT BASED ON THE WEIGHT OF THE ADDED WATER. 